Networks have become ubiquitous. One type of network is known as a wireless ad hoc network. A wireless ad hoc network is a decentralized wireless network. The network is ad hoc because it does not rely on a preexisting infrastructure, such as routers in wired networks or access points in managed (infrastructure) wireless networks. Instead, each node participates in routing by forwarding data for other nodes, and so the determination of which nodes forward data is made dynamically based on the network connectivity. The decentralized nature of wireless ad hoc networks makes them suitable for a variety of applications where central nodes can't be relied on, and may improve the scalability of wireless ad hoc networks compared to wireless managed networks. Minimal configuration and quick deployment make ad hoc networks suitable for emergency situations like natural disasters or military conflicts.
An ad-hoc network is made up of multiple nodes connected by links. Links are influenced by the node's resources (e.g. available energy supply, transmitter power, computing power and memory) and by behavioral properties (e.g., reliability and trustworthiness), as well as by link properties (e.g. line-of-sight interference, length-of-link and signal loss, interference and noise). Since new and old links can be connected or disconnected at any time, a functioning network must be able to cope with this dynamic restructuring, preferably in a way that is timely, efficient, reliable, robust and scalable.
The network must allow any two nodes to communicate, often via other nodes that relay the information. A path is a series of links that connects two nodes. Often there are multiple paths between any two nodes. Many of these applications utilize battery-powered nodes whose uninterrupted service life is limited by the energy efficiency of the node itself. As battery technology is not expected to make significant gains in the near future, there has been a wealth of research into software and hardware methods for reducing total energy consumption for multihop wireless networks.
RADAR (radio detection and ranging) is an object detection system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, terrain and people. A radar system has a transmitter that emits radio waves. When they come into contact with an object they are scattered in all directions. The signal is thus partly reflected back and it has a slight change of wavelength (and thus frequency) if the target is moving. The receiver is usually, but not always, in the same location as the transmitter. Although the signal returned is usually very weak, the signal can be amplified through use of electronic techniques in the receiver and in the antenna configuration. This enables a radar unit to detect objects at ranges where other emissions from the target object, such as sound or visible light, would be too weak to detect. Radar uses include meteorological detection of precipitation, measuring ocean surface waves, air traffic control, police detection of speeding traffic, and military applications.